In existing power tools, in order to brake an electric motor quickly, a connecting terminal of the electric motor is often short-circuited when disconnected from a power source, so that the electric motor generates self-induced current due to inertia, and the electric motor is decelerated quickly under an action between a magnetic field generated in coils by the self-induced current and a magnetic field of the electric motor itself. However, great energy loss may be caused in this way.